(1) Field of the Invention
This invention relates to a method of detecting defects caused by a silicon nitride etching step in order to stop processing defective wafers and control the silicon nitride etching step. More particularly the invention relates to the use of a scanning electron microscope evaluation of test wafers treated with potassium hydroxide after the test wafers have passed through the silicon nitride etching step.
(2) Description of the Related Art
A patterned layer of silicon nitride formed over a layer of pad oxide is often used as a mask in the manufacture of semiconductor integrated circuit wafers. The pattern is formed in the silicon nitride layer using dry etching and control of this etching step is both important and difficult. This invention provides a method of detecting defects due to the silicon nitride etching step using a potassium nitride treatment and scanning electron microscope evaluation of a test wafer. This early detection of defects provides a means to control the silicon nitride etching step.
U.S. Pat. No. 5,362,356 to Schoenborn describes methods for monitoring film removal during plasma etching. Silicon nitride is one of the materials that can be monitored using the methods described by Schoenborn. The control methods described by Schoenborn are different from the method described in this patent application which uses a test wafer for monitoring a lot of N wafers.